How LOG() Works in MariaDB

In MariaDB, LOG() is a built-in function that returns the natural logarithm of its argument to a given base.

It can be called with one or two arguments:

When called with one argument, returns the natural logarithm of the argument.
When called with two arguments, returns the logarithm of the second argument to the base specified in the first argument.

When called with a single argument, LOG() is the inverse of EXP(), and it’s the same as using LN().

Syntax

The function can be used in the following two ways:

LOG(X)
LOG(B,X)

When using the first syntax, the function returns the natural logarithm of X.

When using the second syntax, the function returns the logarithm of X to the base B.

Example – Single Argument Syntax

Here’s an example that uses the single argument syntax:

SELECT LOG(3);

Result:

+--------------------+
| LOG(3)             |
+--------------------+
| 1.0986122886681098 |
+--------------------+

Here’s what we get when we pass e:

SELECT LOG(2.718281828459045);

Result:

+------------------------+
| LOG(2.718281828459045) |
+------------------------+
|                      1 |
+------------------------+

The number e, also known as Euler’s number, is a mathematical constant approximately equal to 2.718281828459045… and so on.

Example – Two Argument Syntax

Here’s an example that uses the two argument syntax:

SELECT LOG(10, 3);

Result:

+--------------------+
| LOG(3)             |
+--------------------+
| 1.0986122886681098 |
+--------------------+

Here’s the same value using different bases:

SELECT 
    LOG(8, 3),
    LOG(16, 3),
    LOG(2, 3);

Result:

+--------------------+--------------------+--------------------+
| LOG(8, 3)          | LOG(16, 3)         | LOG(2, 3)          |
+--------------------+--------------------+--------------------+
| 0.5283208335737188 | 0.3962406251802891 | 1.5849625007211563 |
+--------------------+--------------------+--------------------+

Argument Ranges

If X is less than or equal to 0, then NULL is returned with a warning.

SELECT 
    LOG(0),
    LOG(-1),
    LOG(16, -3),
    LOG(2, -3);

Result:

+--------+---------+-------------+------------+
| LOG(0) | LOG(-1) | LOG(16, -3) | LOG(2, -3) |
+--------+---------+-------------+------------+
|   NULL |    NULL |        NULL |       NULL |
+--------+---------+-------------+------------+
1 row in set, 4 warnings (0.001 sec)

Let’s check the warnings:

SHOW WARNINGS;

Result:

+---------+------+---------------+
| Level   | Code | Message       |
+---------+------+---------------+
| Warning | 1365 | Division by 0 |
| Warning | 1365 | Division by 0 |
| Warning | 1365 | Division by 0 |
| Warning | 1365 | Division by 0 |
+---------+------+---------------+

Also, the base must be greater than 1. If not, NULL is returned:

SELECT 
    LOG(0, 3),
    LOG(1, 3),
    LOG(-1, 3);

Result:

+-----------+-----------+------------+
| LOG(0, 3) | LOG(1, 3) | LOG(-1, 3) |
+-----------+-----------+------------+
|      NULL |      NULL |       NULL |
+-----------+-----------+------------+
1 row in set, 3 warnings (0.000 sec)

Check the warnings:

SHOW WARNINGS;

Result:

+---------+------+---------------+
| Level   | Code | Message       |
+---------+------+---------------+
| Warning | 1365 | Division by 0 |
| Warning | 1365 | Division by 0 |
| Warning | 1365 | Division by 0 |
+---------+------+---------------+

Non-Numeric Arguments

Here’s an example of what happens when we provide non-numeric arguments:

SELECT LOG('Homer', 'Simpson');

Result:

+-------------------------+
| LOG('Homer', 'Simpson') |
+-------------------------+
|                    NULL |
+-------------------------+
1 row in set, 2 warnings (0.000 sec)

Let’s see the warning:

SHOW WARNINGS;

Result:

+---------+------+-------------------------------------------+
| Level   | Code | Message                                   |
+---------+------+-------------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'Homer' |
| Warning | 1365 | Division by 0                             |
+---------+------+-------------------------------------------+

Null Arguments

LOG() returns null if any argument is null:

SELECT 
    LOG(null),
    LOG(null, 3),
    LOG(16, null),
    LOG(null, null);

Result:

+-----------+--------------+---------------+-----------------+
| LOG(null) | LOG(null, 3) | LOG(16, null) | LOG(null, null) |
+-----------+--------------+---------------+-----------------+
|      NULL |         NULL |          NULL |            NULL |
+-----------+--------------+---------------+-----------------+

Missing Arguments

Calling LOG() with the wrong number of arguments, or without any arguments results in an error:

SELECT LOG();

Result:

ERROR 1582 (42000): Incorrect parameter count in the call to native function 'LOG'

And:

SELECT LOG(10, 2, 3);

Result:

ERROR 1582 (42000): Incorrect parameter count in the call to native function 'LOG'